1. Field of the Invention
The invention is directed to a method and a device for testing a security element of a security document.
2. Brief Description of the Related Art
Value or security documents can contain one or a plurality of security elements, it being possible to ascertain, for example, the authenticity of the value or security document as a function of a verification of a security element. In order to be able to identify, say, counterfeits of such documents, it is desirable to create methods and devices for the reliable testing of such security elements.
It is known that value or security documents can contain so-called effect pigments. These effect pigments can configure a security element, or be part of a security element. EP 1 748 903 B1, for example, describes a machine-readable security element for security products. This publication describes optically variable platelet-shaped effect pigments which, from at least two different angles of illumination or observation, display at least two and at most 4 optically clearly distinguishable discrete colours. The security element can also contain at least one particle-like substance with electroluminescent properties.
DE 10 2007 063 415 A1 discloses a method and a corresponding device for recognising a product or information concerning the product. This method identifies a hidden coding carried by the product; the coding is given by a set of ellipsometric parameters and the method comprises the following steps:                measuring ellipsometric variables for at least one defined point on a surface of the product,        comparing the measured ellipsometric variables with at least one previously archived coding and        finding a match between the measured ellipsometric variables and the archived coding or one of the archived codings, or finding a non-match with every archived coding.        
U.S. Pat. No. 6,473,165 B1 discloses an automated verification system for authenticating an object with an optical security feature. The verification system comprises an optical system, a transport apparatus and an analyser. The optical system comprises one, or a plurality of, light sources for generating a narrow-band or broad-band light beam. The transport apparatus interacts with the light sources and is configured in such a way that the object is positioned so that one, or a plurality of, light beams strike a section in which the security feature is to be arranged. The analyser receives the light beams reflected by, or which pass through, the object and is adapted so that optical properties of the light beams can be analysed at different angles and/or wavelengths in order to verify the object's authenticity.
A verification can be effected as a function of the effects produced by the optically variable effect pigments. For example, a colour shift effect produced by the optically variable effect pigments is available for verification.
Nevertheless, verifying an effect produced by optically variable effect pigments, in particular the colour shift effect, can be difficult or impossible in certain fields of application. It is also possible for the effect produced by optically variable effect pigments such as the colour shift effect to be imitated with the help of other effect pigments. Thus the optical verification methods which work on the basis of the produced effect can verify one optically variable effect pigment even though another effect pigment is in fact present, resulting in a false verification.
The use of optically variable effect pigments as field displacement elements together with electroluminescent pigments is also known. Electroluminescent pigments facilitate a verification as a function of emitted electroluminescent radiation when such an electroluminescent pigment is excited, e.g. by an electrical field. Such an excitation and verification can also be difficult or even impossible in many application scenarios, such as bank ATMs. Here it can be desirable to perform a verification independently of electroluminescent radiation.
There is therefore the technical need of providing a method and a device for the reliable verification of a security element of a value or security document which both allow reliable testing and broaden the scope within which such testing can be used.